1. Field of the Invention
The present invention is broadly concerned with methods for synthesizing various epothilone segments or precursors (either naturally occurring or analogs thereof) which can be used for the efficient synthesis of complete epothilones. More particularly, the invention pertains to such synthesis methods wherein, inter alia, the epothilone segment C is prepared using a unique Noyori reduction scheme, and epothilone segments B and C are connected via a novel aldol condensation reaction. These syntheses can be used to prepare the naturally occurring segments and a wide variety of corresponding analogs and homologs.
2. Description of the Prior Art
The epothilones (16-membered macrolides which were initially isolated from the myxobacterium Sorangium cellulosum) represent a class of promising anti-tumor agents, and have been found to be potent against various cancer lines, including breast cancer cell lines. These agents have the same biological mechanism of action as Taxol, an anti-cancer drug currently used as a primary therapy for the treatment of breast cancer. Other potential applications of the epothilones could be in the treatment of Alzheimer's disease, malaria and diseases caused by gram-negative organisms. Other cancers such as ovarian, stomach, colon, head and neck and leukemia could also potentially be treated. The epothilones also may have application in the treatment of arthritis.
In comparison to Taxol.RTM., the epothilones have the advantage of being active against drug-resistant cell lines. Drug resistance is a major problem in chemotherapy and agents such as the epothilones have overcome this problem and hold great promise as effective agents in the fight against cancer.
In addition, the poor water solubility of Taxol.RTM. has led to the formulation of this drug as a 1:1 ethanol-Cremophor concentrate. It has been determined that the various hypersensitive reactions in patients such as difficulty in breathing, itchiness of the skin and low blood-pressure are caused by the oil Cremophor used in the formulation. The epothilones are more water soluble than Taxol.RTM. which has positive implications in its formulation. Further advantages of the epothilones include easy access to multi-gram quantities through fermentation procedures. Also the epothilones are synthetically less complex, thus structural modifications for structure activity relationship studies are easily accessible.
The epothilones exhibit their activity by disrupting uncontrolled cell division (mitosis), a characteristic of cancer, by binding to organelles called microtubules that are essential for this process. Microtubules play an important role in cell replication and disturbing the dynamics of this component in the cell stops cell reproduction and the growth of the tumor. Antitumor agents that act on the microtubule cytoskeleton fall into two general groups: (1) a group that inhibits microtubule formation and depolymerizes microtubules and, (2) a group that promotes microtubule formation and stabilizes microtubules against depolymerization. The epothilones belong to the second group and have displayed cytotoxicity and antimitotic activity against various tumor cell lines.
It has been demonstrated on the basis of in vitro studies that the epothilones, especially epothilone B, are much more effective than Taxol.RTM. against multi-drug resistant cell line KBV-1. Preliminary in vivo comparisons with Taxol.RTM. in CB-17 SCID mice bearing drug-resistant human CCRF-CEM/VBL xenografts have shown that the reduction in tumor size was substantially greater with epothilone B in comparison to Taxol.RTM..
In light of the great potential of the epothilones as chemotherapeutic agents, there is a need for techniques allowing the practical, large scale, economical synthesis thereof. Furthermore, there is a need for synthesis methods which facilitate the preparation of various homologs and analogs of the known epothilones, and those having affinity labels allowing study of the binding interactions of these molecules.